Polymeric materials that are reinforced with insoluble materials such as, for example, fibers or particulate materials are generally referred to as “polymer composites” or simply as “composites”. In recent years, one type of composite termed a “nanocomposite” has come into widespread use. By definition, a nanocomposite has a reinforcing material that has one or more dimensions on the order of a nanometer. One type of nanocomposite has an exfoliated layered silicate as the reinforcing material wherein the layered structure is broken up and individual silicate platelets are dispersed throughout the polymeric resin.
Layered silicates are generally composed of stacked silicate platelets. The individual silicate platelets typically have a thickness on the order of about one nanometer and an aspect ratio of at least about 100. The spaces between the silicate platelets are called “gallery spaces”. Under the proper conditions, the gallery spaces can be filled with a material such as, for example, a polymer. The material swells the layered silicate, increasing the distance between silicate platelets in a process termed “intercalation”. If the layered silicate swells sufficiently such that at least some of the individual silicate platelets are no longer organized into stacks, those individual silicate platelets are said to be “exfoliated”.
The degree to which a polymer will intercalate and/or exfoliate a particular layered silicate typically depends on the compatibility of the polymer with the layered silicate. For example, polymers having groups that are compatible with the layered silicates may intercalate and/or exfoliate layered silicates. On the other hand, some polymers such as, for example, non-polar polymers (e.g., polyethylene, polypropylene) may not readily intercalate or exfoliate layered silicates due to a lack of compatibility with the layered silicate.